Cytology is a branch of biology dealing with the study of the formation, structure, and function of cells. As applied in a laboratory setting, cytopathologists, cytotechnologists, and other medical professionals make medical diagnoses of a patient's condition based on visual examination of a specimen of the patient's cells. A typical cytological technique is a “pap smear” test, in which cells are scraped from a woman's cervix and analyzed in order to detect the presence of abnormal cells, a precursor to the onset of cervical cancer. Cytological techniques are also used to detect abnormal cells and disease in other parts of the human body.
Cytological techniques are widely employed because collection of cell samples for analysis is generally less invasive than traditional surgical pathological procedures such as biopsies, whereby a tissue specimen is excised from the patient using specialized biopsy needles having spring loaded translatable stylets, fixed cannulae, and the like. Cell samples may be obtained from the patient by a variety of techniques including, for example, by scraping or swabbing an area, or by using a needle to aspirate body fluids from the chest cavity, bladder, spinal canal, or other appropriate area. The cell samples are placed in solution and subsequently collected and transferred to a glass slide for viewing under magnification. Fixative and staining solutions may be applied to the cells on the glass slide for preserving the specimen for archival purposes and for facilitating examination.
It is generally desirable that the cells on the slide have a proper spatial distribution, so that individual cells can be examined. A single layer of cells is typically preferred. Accordingly, preparing a specimen from a fluid sample containing many cells typically requires that the cells first be separated from each other by mechanical dispersion, fluidic shear, or other techniques so that a thin, monolayer of cells can be collected and deposited on the slide. In this manner, the cytotechnologist can more readily discern abnormal cells. The cells are also able to be counted to ensure that an adequate number of cells have been evaluated.
Certain methods, apparatus, and materials for generating a thin monolayer of cells on a slide advantageous for visual examination are disclosed in U.S. Pat. No. 5,143,627 issued to Lapidus et al. and entitled “Method and Apparatus for Preparing Cells for Examination;” U.S. Pat. No. 5,240,606 issued to Lapidus et al. and entitled “Apparatus for Preparing Cells for Examination;” and U.S. Pat. No. 5,256,571 issued to Hurley et al. and entitled “Cell Preservative Solution,” all of which are assigned to the assignee of the present invention and all of the disclosures of which are incorporated herein by reference in their entirety.
According to one method disclosed in these patents, a patient's cells in a preservative fluid in a sample container are dispersed using a spinning sample collector disposed therein. A controlled vacuum is applied to the sample collector to draw the fluid through a screen filter thereof until a desired quantity and spatial distribution of cells is collected against the filter. Thereafter, the sample collector is removed from the sample container and the filter portion impressed against a glass slide to transfer the collected cells to the slide in substantially the same spatial distribution as collected.
While apparatus manufactured according to the teachings of one or more of these patents have been commercially successful, such as the ThinPrep® 2000 System manufactured and sold by Cytyc Corporation located in Boxborough, Mass., such apparatus requires substantially constant attendance by a trained operator. For example, for each specimen to be prepared, the operator must load the system with an open sample vial containing the patient's cells in preservative fluid, a sample collector with filter, a glass slide, and an open fixative bath vial containing a fixative solution. The system then cycles automatically, the cells being dispersed by the sample collector, collected against the filter, and transferred to the slide. The slide is then automatically deposited in the fixative bath vial where it must be retrieved by the operator for manual loading in a staining rack for further processing. Thereafter, the sample vial and sample collector must be removed from the system, to avoid inter-sample contamination, before replacements and a new slide are installed to produce another specimen from a different patient's sample.
Once a specimen is prepared, fixed, and stained, the specimen may be manually visually inspected by a cytotechnologist, typically under magnification, and with or without various sources of illumination. Alternatively or additionally, automated machine vision systems have been adapted to aid cytological inspection. For example, an automated vision system may perform a preliminary assessment of the entire slide on which the specimen is disposed to alert the cytotechnologist to potentially the most relevant areas of the slide for close inspection, or may be used to rescreen specimens already analyzed by the cytotechnologist.